Ringing Suppression for Ultrasonic Nondestructive Testing using Iterative Learning Control and H-infinity Synthesis

Abstract

In this work, the use of iterative learning control (ILC) in ringing suppression is assessed with the intention of generating precise ultrasonic wave pulses for nondestructive testing (NDT) purposes. The premise of ILC is that the performance of a system, which is repetitively executing the same task, can be improved by learning from previous attempts. In order to develop a systematic approach to the design of the L- and Q-filters for the ILC, a previously proposed H∞-synthesis method is employed. To this end, an experimental frequency analysis is conducted for commonly used ultrasound transducers, and a low-order model is fitted to the resulting data near the transducer’s peak frequency. Based on this model, appropriate L- and Q-filters are synthesized and the ILC is trained to generate the desired wave packet. The simulation results indicate convergence of the proposed ILC algorithm, and thus generate the necessary driving trajectory. By taking the generated signal from simulation and using it as the driving signal in laboratory experiments, it is shown that ringing effects, i.e. distortions of the induced wave packets, are significantly reduced. The impact of such an improvement in the context of guided ultrasonic NDT is demonstrated through a time-of-flight experiment for edge detection, showing promising results and a positive starting point for future work.